This invention relates to a torque limiting clutch. More particularly, this invention relates to a clutch coupling a driven member and a driving member for rotation in unison while transmitting torque therebetween up to a predetermined torque limit of the clutch. When the torque limit of the clutch is reached, the clutch slips to allow relative rotation of the driving and driven members while transmitting the predetermined torque therebetween.
Clutches of this nature find wide application in a variety of mechanical arts. For example, power driven assembly tools which are used to drive threaded fasteners usually incorporate a torque limiting clutch to prevent over tightening of the fasteners. Such clutches also find application in aircraft where they are used in servo systems. Servo systems are used in aircraft to perform a variety of functions. For example, servo systems may be employed to extend and retract the aircraft landing gear or move engine thrust reversing devices between stowed and deployed positions. Further, an aircraft may have servo systems which moves aerodynamic surfaces of the aircraft between selected positions. In all of these illustrative servo systems, and others, torque limiting clutches may be used to prevent damage to the aircraft structure and to the servo system drive train in the event that a jam prevents movement of the system.
In view of the wide application of torque limiting clutches, a number of desirable characteristics for such clutches have been recognized. Among these desirable characteristics are a smooth transition from driving to slipping torque transmission, a repeatable torque limit so that the clutch begins to slip at substantially the same torque time after time, and a mechanically simple and physically rugged clutch structure which is relatively inexpensive to manufacture. Further, a torque limiting clutch should be easily calibrated during manufacture so that compensation may be made for tolerance stack up of its component parts which effect the torque limit of the clutch. Finally, the clutch should be such that wear occurring during the life of the clutch has only an acceptably small effect upon the torque limit of the clutch.
Because of the many desirable characteristics for a torque limiting clutch, conventional clutches of this type have been deficient in one or more respects. Accordingly, it is a primary object for this invention to provide a torque limiting clutch which avoids or ameliorates one or more of the deficiencies of conventional torque limiting clutches.
Another object for this invention is to provide a torque limiting clutch having a driven member and driving member coupled by a multitude of friction elements the number of which may be changed to calibrate the torque limit of the clutch.
Still another object is to provide a method of calibrating a torque limiting clutch according to this invention.
Yet another object is to provide a torque limiting clutch which effects a smooth transition from driving to slipping torque transmission.
Another object for this invention is to provide a torque limiting clutch which has a substantially constant torque limit throughout its service life.
Still another object is to provide a torque limiting clutch which is mechanically simple in construction and physically rugged.
In summary, this invention provides a torque limiting clutch having a number of axially stacked resilient friction elements interposed between a driven member and a driving member. The friction elements are dislorted to resiliently and frictionally engage one of the members and mechanically interlock with the other member. When torque is applied to either one of the members, the resilient elements transmit the torque to the one member. The nature of the interlocking fit of the resilient elements with the other member is such that the transmitted torque urges the resilient elements away from engagement with the one member. So long as the transmitted torque is less than a predetermined value the preload of the resilient elements prevails and relative rotation of the members is prevented. When the transmitted torque reaches the predetermined value, the torque prevails over the preload of the resilient elements so that they slip relative to the one member. Thus, relative rotation of the driving and driven members is permitted while the predetermined torque is transmitted therebetween.
One preferred embodiment of the invention is described in detail below with reference to drawing figures which illustrate only this one preferred embodiment.